Diesased trees in a forest
Forests

Recognizing Root Rot

(#2 in a series coming out of the Cortes Forestry General Partnership’s 2022 AGM)

According to BC Hydro, more than half the province’s power outages are caused by falling trees. That number is probably higher on Cortes and Quadra Islands, which are heavily forested. Trees appear to be dropping on the power lines every time there is a storm. There are also large numbers of relatively young trees falling over in the forest, and in people’s yards. Some of them were critically weakened by root rot. 

In yesterday’s interview, General Manager Mark Lombard said a significant number of the fir trees that Cortes Forestry General Partnership recently harvested were afflicted by root rot.  

So Cortes Currents asked, “how do you recognize root rot?”

Douglas-fir stump with bark removed to show (Armillaria) root rot fans – courtesy Managing Root Disease in British Columbia, Ministry of Forests

Lombard suggested,  “Look at the fir trees. In a healthy fir tree, the crown will be green and typically fairly uniform and vibrant. It’s very similar to a house plant or any plant that you have in the garden. If you look at a plant that has brown on the leaves or the leaves are curled up, or the plant looks yellowish, you can tell it’s not very healthy as opposed to the really healthy plant that’s green and flowering. It’s the exact same thing with the fir trees, or any of the trees.”

Hemlock are particularly susceptible to mistletoe, and red cedar to drought. 

Root rot is one of the principle threats to Douglas Fir.

Some of the victims are immediately recognizable among the wind blown trees in the forest. 

“Sometimes you’ll see a fir tree that has fallen over and there’s just a little nub of a root. There’s hardly any lateral roots that came up and not much soil. That’s a sign of root rot,” explained Lombard. “Another kind of root rot can make the tree rot in the stump and just up the first couple of meters of the stem. So sometimes you’ll see a fir tree that shattered and broke off. If you look carefully, you’ll notice that there’s just the outer sapwood ring left, and the heartwood has rotted away. When it falls over the sapwood shatters.  You can see the tree broken off, which is unlikely because fir is such a strong tree. Those are some of the signs of root rot, and it’s not always easy to see.” 

While most often found in Douglas fir, Root rot can also be found in hemlock (photo above) – courtesy Managing Root Disease

The BC Ministry of Forests handbook ‘Managing Root Disease in British Columbia’ lists a number recommended treatments. 

  1. Replant the area with species less susceptible to root rot
  2. ‘Stump removal has been shown to reduce root rot disease in the majority of cases where it has been applied.’ 
  3. Pushover harvesting has been shown to be as effective as stump removal
  4. ‘Hardwoods are less susceptible to infection and more tolerant to disease.’ The roots of birch in particular ‘can form a barrier to underground disease movement.’
  5. Biological controls are introduced agents that can displace or prevent colonization by pathogenic fungi and prevent the spread of disease.
Distribution of Phellinus weirii, also known as Phellinus sulphurascens – courtesy Managing Root Disease in British Columbia
Distribution of Armillaria ostoyae – courtesy Managing Root Disease in British Columbia

Lombard said the most prevalent root rots on Cortes Island are Armillaria ostoyae and Phellinus weirii.

He suggested people wanting more information look up Dr Suzanne Simard from UBC, who’s doing the Mother Tree Project and Paul Stamets who has been researching fungi for years.

Top image credit: Dead and symptomatic trees killed by Phellinus Weirii –courtesy Managing Root Disease in British Columbia

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